1. Technical Field
The present disclosure relates to reset circuits for electronic devices, and particularly to a reset circuit having stable outputs.
2. Description of Related Art
Many electronic devices use reset circuits for initialization. Generally, when an electronic device is turned on, a reset circuit of the electronic device does not need to generate reset signals for the electronic device as a first step. After waiting for a predetermined delay time to ensure that the electronic device has already been supplied with working electric power as normal, the reset circuit should generate the reset signals, such that the electronic device can be properly initialized.
RC delay circuits are often used in the reset circuits for achieving the aforementioned effect. FIG. 2 shows a typical reset circuit, which includes a power supply VCC, a resistor R, a capacitor C, a Schmitt trigger U11, and an inverter U12. The resistor R and the capacitor C are connected in series between the power supply VCC and ground. An input end of the Schmitt trigger U11 is connected between the resistor R and the capacitor C, and an output end of the Schmitt trigger U11 is connected to an input end of the inverter U12. An output end of the inverter U12 is used to provide a reset signal to an electronic device (not shown). In use, the power supply VCC charges the capacitor C via the resistor R. After waiting for a predetermined delay time to ensure that the electronic device has already been supplied with normal working electric power, the voltage of the capacitor C reaches a threshold voltage of the Schmitt trigger U11, and thus the Schmitt trigger U11 is turned on. The capacitor C discharges through the Schmitt trigger U1 (i.e., inputs a predetermined logic 1 signal to the Schmitt trigger U11), and the Schmitt trigger U11 correspondingly outputs a predetermined logic 0 signal. The inverter U12 receives the logic 0 signal and correspondingly outputs a logic 1 signal to the electronic device as the reset signal.
During the delay time (i.e., when the capacitor C is being charged), the voltage of the capacitor C is not high enough to turn on the Schmitt trigger U11, and the capacitor C is unable to discharge. Therefore, if the power supply VCC is by mistake or otherwise turned off during the delay time, charges may remain in the capacitor C. The next time the reset circuit is used, the residual charges may interfere with the charging and discharging processes of the capacitor C, and thus the delay and application times of the reset circuit may be changed.
Therefore, there is room for improvement within the art.